Repurposing Dantrolene for Long-term Combination Therapy to Potentiate Antisense-Mediated DMD Exon-Skipping in the mdx mouse

Duchenne muscular dystrophy (DMD) is caused by mutations in DMD, resulting in loss of dystrophin, essential to muscle health. DMD “exon-skipping” uses anti-sense oligo-nucleotides (AON) to force specific exon exclusion during mRNA processing to restore reading frame and rescue of partially functional dystrophin protein. While exon-skipping drugs in humans show promise, levels of rescued dystrophin protein remain suboptimal. We previously identified dantrolene as a skip-booster when combined with AON in human DMD cultures and short-term mdx dystrophic mouse studies. Here we assess the effect of dantrolene/AON combination on DMD exon-23 skipping over long-term mdx treatment under conditions that better approximate potential human dosing. To evaluate dantrolene/AON combination treatment effect on dystrophin induction, we assayed three AON doses, with and without oral dantrolene, to assess multiple outcomes across different muscles. Meta-analyses of the results of statistical tests from both quadriceps and diaphragm assessing contributions of dantrolene beyond AON, across all AON treatment groups provide strong evidence that dantrolene modestly boosts exon-skipping and dystrophin rescue, while reducing muscle pathology in mdx mice (p<0.0087). These findings support trial of combination dantrolene/AON to increase exon-skipping efficacy and highlight the value of combinatorial approaches and FDA drug re-purposing for discovery of unsuspected therapeutic application and rapid translation.